Single sideband transmitter



Jan. 12, 1954 1.. R. KAHN SINGLE SIDEBOARD TRANSMITTER 5 SheetsSheet 1 Filed Aug. 16, 1951 TIME m W NK R R m mm H A 3M w L 5 W C 0 i! w Jan. 12, 1954 1.. R. KAHN SINGLE SIDEBOARD TRANSMITTER 5 Sheets-Sheet 2 Filed Aug. 16, 1951 Jan. 12, 1954 L. RKAHN SINGLE SIDEBOARD TRANSMITTER 5 Sheets-Sheet 6 Filed Aug. 16, 1951 INVENTOR LEUNARD RKAHN ATTORNEY Jan. 12, 1954 Filed Aug. 16, 1951 2754 19/ A i/Wdik 2'2 L. R. KAHN 2,666,133

SINGLE SIDEBOARD TRANSMITTER 5 Sheets-Sheet. 4

INVENTOR LEUNARD RKAHN ATTO R N EY Jan. 12, 1954 Filed Aug. 16, 1951 l R. KAHN SINGLE SIDEBOARD TRANSMITTER LEUNARD RKAI-IN 5 Sheets-Sheet 5 Patented Jan. 12, 1954 SINGLE SIDEBAND TRANSMITTER Leonard R. Kahn, New York, N. Y., assignor to Radio Corporation-of America, a corporation of Delaware Application Augustlfi, 1951, Serial No. 242,061

26 Claims.

This invention relates to transmitters, and more particularly to single sideband (SSE) transmitters.

The present application is a continuation-inpart of my copending applications, Serial No. 90,243, filed April 28, 1949, and Serial No. 162,757, filed May 18, 1950, both of which are now abandoned.

In comparing single sideband carrier suppressed systems and double sideband systems, a gain in signal-to-noise ratio of 9 db has been reported for single sideband systems over double sideband systems. It is known that single sideband systems have other advantages such as more effective or more efficient use of the frequency spectrum. The main disadvantage of a conventional single sideband system is the complex and costly equipment which must be used.

The intelligence in a single sideband signal is transmitted by varying two properties of the transmitted wave, namely the amplitude and the phase. The phase variations carry a large number of sidebands with distinct bundles of energy; the amplitude modulation determines the total energy given to the entire signal at anyinstant of time, and also neutralizes some of the sidebands and reinforces others. In order "to pass the amplitude modulation characteristic of the single sideband signal, the conventional single. sideband transmitters must have all stages that amplify the single sideband radio frequency signal adjusted for linear operation.

Linear radio frequency amplifiers are difficult to design, are rather expensive and complex, and are relatively inefficient. Further, linear amplifiers are difficult circuits to adjust, as a result of which dimculties arise in maintenance during normal transmitter operation or when changes are to be made in the tuning of the transmitter.

An object of this invention therefore is to eliminate the necessity of using linear amplifiers on all the radio frequency stages of a single sideband transmitte Another object is to devise a. system by means of which amplifiers of higher efficiency, of less cost, and of relative simplicity, may be used in a single sideband transmitter.

An additional object is to provide an arrangement by means of which class C amplifiersmay be used in a single sideband transmitter; amplifiers of this typ are rather easy to adjust.

A further object of this invention is to make possible easy modification-of existing double sideband amplitude modulated transmitter for sin duction in distortion in such stages.

2 gle sideband; service, thus permitting the use of high level amplitude modulation techniques in single sideband transmitters Without the need for high-level linear amplifiers.

In the conventional single sideband transmitters, which use a large number of linear amplifier stages, difficulties arise when it is attempted to use negative feedback in order to effect a re- In such transmitters, positive feedback often. occurs. This is undesired because such positive feedback sets up oscillations. In the system of this invention in which the number of linear amplifier stages is greatly reduced as compared to conventional systems, the possibility of positive feed-- back is reduced; therefore, negative feedback may be utilized more dependablyin the system of this invention than in conventional single sideband systems.

It is well known that certain difficulties arise if all stages of a transmitter-operate at the same frequency. Such operation at the same frequency may be termed straight frequency operation. If straightfrequency operation is utilized, there is a strong tendency toward regenera tion. Such regeneration or singing is undesirable. The tendency toward regeneration may be reduced by careful shielding. Such shielding, however, is expensive and therefore rather impractical.

Most transmitters employ frequency multiplication to reduce the shielding otherwise necessary. There is much less chance of regeneration if'the entire transmitter does not operate at the same frequency.

The present application discloses a system Which allows frequency multiplication to be utilized in a single sideband transmitter, so that all stages of the transmitter do not have to operate at the same frequency.

Although the present invention will be described in connection with the amplification of single sideband signals, it is equally applicable to the amplification of other forms of hybrid modulated waves. A hybrid modulated Wave may be defined as one which has both amplitude and angular velocity modulation components. Examples of hybrid modulatedwaves are: carrier ppressed double sideband, single sideband, vestigial sideband, and quadrature modulated Waves.

Th foregoing-and other objects and advantages of the invention will be best understood from the following detailed description thereof,

reference being had to the accompanying drawings, wherein:

Figs. 1-4 are diagrams of various types useful in explaining the invention;

Fig. 5 is a block diagram of a single sideband transmitter according to the present invention;

Fig. 6 is a partial block diagram of a modification; and

Figs. 7A, 7B and 7C taken together constitute a detailed circuit diagram of the essential elements of a transmitter according to this inven-.

tion. I

Briefly, the objects of this invention are accomplished in the following manner: A portion of the single sideband wave tobe amplified is passed through several stages of limiters, thereby eliminating the amplitude modulation component and producing the pure phase modulation component. This phase modulated wave is divided in frequency, amplified by highly efficient, non-critical class C amplifiers, heterodyned to a igher frequency, multiplied in frequency and finally amplified to the desired output level, again by class C amplifiers. The original single sideband wave amplitude modulation envelope is detected and the resultant audio frequency Wave is amplified in an audio amplifier and then passed through an amplitude equalizer and a delay network. The amplified detected amplitude modulation envelope then remodulates, in a power amplifier, the amplified phase modulation component, resulting in an amplified copy of the original single sideband wave. If the phase and amplitude modulation components are recombined in proper phase and with proper amplitudes, the undesired sidebands of the phase and amplitude modulation components will cancel, reproducing the single sideband wave form. For any form of intelligence transmission such as voice, in which the amount of energy trans mitted in a given period of time may vary, the unidirectional component of the amplitude modulation component is utilized to correspondingly vary the average output power of the transmitter.

Before describing the transmitter or amplifying system of this invention in detail, it may prove helpful to review the characteristics of a single sideband wave. Fig. 1 shows the spectral distribution of a single sideband wave having equal carrier and sideband amplitudes. The upper sideband is represented in this figure and it represents a signal frequency of 600 cycles, so that F3 is 600 cycles higher than F on the frequency axis.

Fig. 2 is a vector representation of the single sideband wave represented in Fig. 1. The carrier frequency is the reference vector. Thus, the sideband vector revolves past the reference vector at a velocity corresponding to the tonal frequency of the signal, which in our example is 600 cycles. If one considers the resultant of the sideband and carrier vectors, it may be seen that such resultant will vary both in amplitude and angular velocity. Therefore, a single sideband wave has both amplitude and phase modulation components.

Fig. 3 is a representation of the amplitude modulation envelope of the single sideband wave, or the amplitude modulation component of such wave. This envelope has a wave shape which is identical with the shape of the wave derived from a full-wave resistance-loaded rectifier fed with a sine wave input.

Fig. 4 shows the phase modulated component of a single-sideband signal having equal carrier and sideband amplitudes. It is seen, that even though a single sideband transmitter is modulated by pure tone the phase modulation wave shape is not necessarily sinusoidal.

In Fig. 3, it is shown that the amplitude modulation component having signal tone modulation is also not necessarily sinusoidal.

Recently Villard, in an article entitled Composite Amplitude and Phase Modulation in the November 1948 issue of Electronics, pages 86-89, described a transmitter which uses a fairly well-known system of single sideband generation. This system uses independent phase and amplitude modulators to produce a single-sideband signal. Since a pure amplitude modulator produces a sinusoidal envelope shape when a single tone is applied and a phase modulator produces a sinusoidal phase modulation component when a single tone is applied, this system is not capable of generating the wave forms required, which were shown in Figs. 3 and 4. Therefore, a large amount of distortion is to be expected and this distortion was reported by Villard. Another problem associated with th s form of single sideband transmitter is that it is not possible to suppress the carrier to any great extent. Therefore, the saving in power common to suppressed carrier operation is not obtained in this system. 7

The subject invention is theoretically capable of producing undistorted signals. The only limitation as to the quality of the system is the goodness of the equipment.

Similarly, if two single sideband tones, of frequencies A and B, are combined, a resultant wave varying in amplitude and phase at the difierence frequency, A-B, will be produced. Only if one oi the tones is substantially larger than the other will the resultant amplitude and phase modulation be essentially sinusoidal.

Fig. is a block diagram of a system according to this invention which was actually constructed and tested. A single sideband generator i has a modulating signal of any desired type applied to its input. For example, such modulating signal input may consist of two or more multiplexed audio tones, each of which is shifted in frequency in accordance with the intelligence in the corresponding multiplex channel. The generator I produces single sideband tone frequencies from the input audio tones and may consist of one or more balanced modulators supplied with the audio input tones and also with locally-generated wave energy, and in addition bandpass filters for selecting one or the other of the sidebands produced in the modulators. If the upper sideband is selected in generator 5 the output frequency of the generator may be, for example, 150 kc. plus audio tone frequencies.

For simplification, let us consider the case in which a single tone is fed to the input of generator l and let us assume that this tone produces a sideband equal in amplitude to the carrier. Generator l produces a low-power single sideband signal identical with that depicted in Figs. 1, 2, 3 and 4.

The low-power single sideband signal output of generator l is fed through a linear radio frequency amplifier 2 the output of which is fed to two separate channels, the first of which may be termed the phase modulation channel and the other, the amplitude modulation channel. The first or phase modulation channel begins with a limiter 3 to which is fed the amplified single sideband signal output of amplifier. 2.. Limiter} .iszapreferaably a full-wave, biased: germanium' diodeaclipper-limiter of the shuntr-connectedtype.

The limited output ofilimiter.3..is.-applied.toan ampliier t. This amplifier may be either linear or non-linear, but is. preferably. nonelinear or class B, in order to improve its efficiency andre duce the cost of the system. The outputiofamplifier i is fed to a second limiter stage 5, which is preferably exactly similar in construction to limiter 3.

The limiters 3' and 5 operate:toilimitlthe single.

sideband signal applied thereto, removingsub stantially all the amplitude modulation component from such signal, such component not. being removed, of course, where the amplitude of the input tone ortcnes goes through zero; Theree fore, the output of limiteria contains substantially only the phase modulation. componentVofthe original single sideband signal, so thatisuch output is a substantially pure phase modulated wave. The wave output of limiter 5, theenvelope of i which may be substantially flat-topped or square,

is passed through a wide band linear amplifier 6, which must be wide. bandinorder-to faithfully pass the fiat-topped or square wave limiter output.

There are side-frequencycomponentsgenerated in a phase modulatedor frequency modulated generator. Therefore, such components appear in the output of generator I, sincesuch output has in effect a phase modulated component. The number and amplitudes of these side-frequency components depend on the phase modulation index of generator I. According to this invention, the amplitude modulated component and the angular or phase modulated-component sidebands of the phase modulation component channel.

As previously discussed, it is desirable that frequency multiplication be used inthetransmitter in order to eliminate the shielding that .is quite essential in straight frequency operation. If the phase modulation componentsignal atthe output of amplifier i3 were passed throughthe frequency multipliers in the transmitter without firstbeing divided in frequency, the modulation index.

applicable to the phase modulationcomponent signal at the output side of such multiplierswould be different from that. existing at the output of generator i, since in such multiplierstheideviationor phase shift is increased; Inzfact; thexapplicable modulation index at the multipliers output would be. higher than that at the output. of generator l thus, a larger number of'side-frequency components, and components ofdiiferent amplitudes, would be produced .at the multipliers output, as compared to those present at the. output:

of generator i. In such event, since the amplitude variation balancing components are derived from the output of generator I, the undesired Bessel.

phase modulated sidebands would no longer be. balanced out of the phase modulation component channel.

Two cascaded frequency: dividers land; 3, having a total division factor of n, are provided prior to the frequency multipliers inthe transmitteu. whichhave a multiplicationfactor: of. 71'. In :this

way, the modulation index applicable to the outell] put of igenerator: l .is. first :divided .bysn'i and :later;

multiplied .by n. This results in no. net .changein the.modulationt index. applicable to. the; multiplier; output,.as. comparedwith such index. applicableto.

the output of generator, 1. Therefore,. the mod-.1

ulationiindex applicable to the multiplieroutput ismade. such as to enable. balancing out of the undesiredphase modulation component Side?" bands. components are preserved at the transmitteroutput frequency. At the same time, the reduced chances of regeneration provided. by frequency.

multiplication are retained.

In atypical example of this invention, the.

factor n has a value of four, so that a division factor offour is used in the frequency dividers. and a multiplication factor of four is used in the transmitter frequency, multipliers. Frequency divider! is coupled to the output of amplifiertv andhas. a division factor of two, while frequency: divider Bis coupled to the outputof divider 7 and. also hasa division factor of two, sothat a di-.

vision factor of four is provided by dividers land 8. Divider l and divider 8 may each comprise flip-flop counter-type circuit having a differentiating circuit in its input. Continuing with-the typical example, if the single sideband signal outof generator I has a frequency of 150 kc., then.

the output of divider. 8 will be at 37.5 kc.

The phase modulation component of the single sideband signal is divided in frequency by a factor.

of four in dividers and 8. The output of divider Bis a phase modulated signal which can be conveniently amplified by highly efficient class-Carm plifierswithout the introduction of any distortion; The output of divider 8, which is stated above may;

have a mean frequency of 37.5 kc., for example, is fed through a class C amplifier 9 to a bandpass filter H) which removes harmonics of the. 37.5;

kc. frequency. Filter is, may, for example, pass a band 10 kc. wide, centered on 37.5 kc.

Following the passage of the wave through filter l0, the'frequency of the phase modulation component of the single sideband signal isconverted; toxthat used to drive the lower level multiplier stages of the transmitter, which in our example would be one fourth of the output frequency.

This frequency conversion is effected in two.

stages, thefirst being from 37.5 kc. to 250 kc. For

" this stageof the conversion, the 37.5-kc. output of filter [0 is fed to a balanced modulator II, to

Which-isalso fed heterodyning energy of 212.5.

kc. from a crystal oscillator 12. For example, the

modulator ll may comprise a pair ofpentagrid converter tubes connected in a push-pull arrangement, the 37.5-kc. frequency being fed antiphasally to one grid in each of the two tubes and'the 2l2.-5-kc. frequency from oscillator E2 beingsfed.

cophasally to another grid in each of the two tubes. The output of modulator H may have a frequency band of 250:;5 kc.

The 250-kc. output of modulator I I is amplifiedi in a class-B radio frequency amplifier l3 and'is then passed on to the second. frequency conversion stage, wherein the phase modulation com.-

ponent is converted from 250 kc. to the frequency for driving the transmitter multiplier stages, which latter frequency is 1750 kc. in our example. The 250-kc. output of amplifier I 3' is fed to a balanced modulator It, to which is also fedheterodyning energy of 1500 kc. from a high'frequencycrystal oscillator I5. The modulator l4 ispreferably exactly. similar in arrangement to ismodulator ,previously described. The output In other words, the phase modulation.

of modulator it may have a frequency of 1750 kc.

The 1750-kc. output of modulator M is amplified in a class (3 radio frequency amplifier l6 and it is the output of this amplifier which is used to drive the lower level multiplier stages of the transmitter. The output of amplifier [6 may be used as the input to a standard amplitude modulated phone transmitter which is more or less conventional with applicants assignee and which includes a plurality of class C multiplying and amplifying stages in the radio frequency section thereof. Utilizing this invention, the transmitter can be tuned in the normal manner and the transmitter stages can be operated in the usual manner as class C multipliers and amplifiers. In our example, 12 has a value of four, so that a fixed multiplication factor of four is used in the transmitter. The output of amplifier i6 is fed to a frequency multiplier ll having a multiplication factor of four, for example. The output of frequency multiplier i? is a phase modulated wave having a mean frequency of 4 x 1750 kc., or 7 me.

The 7 -mc. output of multiplier ll is amplified to a high level in a class C radio frequency amplifier 53, which may consist of a plurality of stages. Since high power radio frequency amplifier I8 is not required to pass or amplify the amplitude modulation component of the single sideband signal, but instead only the phase modulation component of such signal, this amplifier (and also the multiplier stages in ii) need not be linear and in fact can be of the type known as class C. The use of linear amplifiers for all the high power radio frequency stages of the transmitter has by this invention been made unnecessary, thus enabling the use of less expensive and more efiicient amplifiers.

This completes the description of what has been termed herein the phase modulation channel. The other or second channel, the amplitude modulation channel, will now be described.

The single sideband signal output of amplifier 2 is fed to the amplitude modulation detector H, which is preferably of the diode vacuum tube type. This linear detector functions to rectify the single sideband wave and to remove the audio envelope therefrom, thus isolating the amplitude modulation component from the phase modulation component of the single sideband wave. The output of detector 159 corresponds to the envelope wave shape of the single sideband wave at the output of generator l and therefore the wave shape at such detector output is similar to that of a fullwave rectified sine wave.

The audio frequency envelope of the single sideband wave is amplified by the linear audio amplifier 2%, which is coupled to the output of detector i9. Amplifier 29 must be linear since it is required to amplify faithfully the amplitude modulation envelope. This amplified audio envelope is fed through an amplitude equalizer 2| to a delay network 22. Equalizer 2! is an im pedance network which can be set by means of switches to provide deemphasis and/or preemphasis correction, to compensate for any nonuniformity of the frequency characteristic of the modulator or power amplifier to be later referred to. Delay network 22 may be adjusted to provide various values of time delay for the signal passing therethrough and operates to equalize the time delays in the two channels, the phase modulation and amplitude modulation channels.

The output of network 22 is supplied to the input of the high level amplitude modulator 23 to furnish driving power therefor. 23 amplitude modulates at a high level the phase modulation signal component, derived from the output of amplifier [8, in the modulated power amplifier 24. The envelope wave shape (amplitude modulation component of the SSB signal) of the signal at the output side of modulator 23 is the same as the envelope wave shape at the output side of generator I. Furthermore, the phase modulation component at the output side of amplifier I8 is identical with the phase modulation component at the output of generator i. If the time relationships between the phase and amplitude modulation components are properly maintained, the signal at the output of amplifier 24 will be a pure, high-power single ideband wave. More in particular, when the delay network 22 is correctly adjusted to equalize the time delays in the two channels and when the amplitude equalizer 2| is properly adjusted to give the proper amplitude of audio wave as applied to modulator 23, the amplitude modulation and phase modulation components retain the original phase relationship of the single sideband wave; under these conditions, sufiicient high level amplitude modulation is effected in 24 to reproduce the form of the original SSE signal, thus cancelling the spurious sidebands introduced when the signal is split into its two components.

The signal at the output of power amplifier 24, which as stated is a pure, high-power single sideband wave, may be transmitted by a suitable transmitting antenna 25 which is coupled to the output of amplifier 24. In our illustrative example, this is a single sideband signal having a nominal frequency of 7 mo., the frequency of the input to amplifier 18.

Although the delay network 22 is illustrated as being in the amplitude modulation channel, it is desired to be pointed out that it could instead be placed in the phase modulation channel if necessary, since the purpose of this network is to equalize the time delays of the signals in the two channels. Therefore, if the signal time delay in the amplitude modulation channel is greater than that in the phase modulation channel, the delay network 22 would be inserted somewhere in the phase modulation channel.

It is quite often desirable to transmit a suppressed carrier along with the single sideband signal. For this purpose, a crystal-controlled carrier frequency, of relatively low amplitude or power level, may be supplied to amplifier 24, to be radiated from antenna 25 along with the single sideband signal.

The system of Fig. 5 will operate in an optimum manner when the average signal energy to be transmitted is constant over a certain interval of time, say 0.1 second or more. Frequencyshifted frequency division multiplex signals are in this constant-average-amplitude category and can be effectively transmitted by the system of Fig. 5. However, if the average level of the amplitude modulation varies the spurious sidebands will not remain balanced at the output of amplifier 25 and the Fig. 5 system will not work in an optimum fashion. For example, voice waves are not of constant average amplitude and an additional circuit is required in Fig. 5 for transmission of this form of intelligence. Also, this varying-average-amplitude condition comes into play in certain cases with frequency shift tones. For example, assume that two equal-amplitude tones are being transmitted at a fixed input level and that the amplitude level is adjusted to bal- Modulator ance= out the. spurious sidebands at the outputsof amplifier 24. Then, if the inputlevel of both tones isreducedto half its previous value, the relative level or" the phase modulation component would remain the same but the amplitude modulation component wouldhave to be increased to two times its former level, or increased by 6 db, to maintain the balance for cancelling out the spurious sidebands. Similarly, if a number .of frequency shift tones were transmitted at a fixed level and the average leveloi amplitude modulation envelope varies, the balance of the spurious sidebands would also vary.

Fig. 6 illustrates a circuit. arrangement which can replace that portion of Fig. shown within the dotted line box B. In Fig. 6 there is an additional circuit which is necessary for effective transmission of varying-average-amplitudc signals by the transmitter of this invention. Such circuit is an output level control 2% which is used to vary the average output power of the transmitter by controlling one of the electrode voltages of power amplifier'il i. Level control circuit 25 takes the form of a series of direct current amplifiers supplied with direct current output from amplitude modulation detector 59, such direct current output correspondingto the average amplitude of the input intelligence. The amplified output from unit 25 controls one of the electrode voltages of the modulated power amplifierl'i i. One possible method of controlling such one electrode voltage would be the varying of the firing angle of the thyratron rectifiers in the power supply for such one electrode.

To give an example of the operation of level control 2t, ii the carrier is suppressed 29 db for the single sidehand carrier-suppressed system and there is no one speaking on the circuit, the direct current output of the amplitude modulation detector is will be very low; in this case, the output level control 2% will make the modulated amplifierfi lgive low output. On the other hand, if voice appears on the circuit, the direct current output of detector i9 will increase and output levelcontrolzt willcause modulated amplifier 24 to give increased output. In a similar manner, all levels of input signal energy will appear in true single sideband form at the output of amplifier 2 3.

In order to maintain'good spurious sideband suppression, it is necessary that the modulator have certain characteristics.

For a transmitter having distortion suppression to the point where all spurious output is 35 dbor more below the signal output of the transmitter, the modulator 23 must be able to pass the second and third harmonics of the-difference between the highest frequency and lowest frequency signals which have appreciable energy. For 25 db spurious output suppression, only'the second harmonic is required to be passed.

For example, assume that it is desired'to transmit the following tone frequencies: 1105, 1275, 1445, 1615, 1785, 1955, 2125, and 2295 cycles. Tones of these values could beused taprovide a four-channel frequency/shift frequency division multiplex signal. The highest frequency difference between large-amplitude signalcomponents is 1190 cycles (2295minus 1105) The carrier amplitude is normally quitesmall and therefore does not enter into the calculations. If a signal having 25-db suppression of-spurious output is required, the modulator 23 must-be equalized for phase-and amplitude characteristics from-at least l lil cycles to.'2380cycles;(170 cycles being the smallest dii ference frequency"between toneseand 2880 cycles 10 being two times the highest frequency difference) If 35 db spurious suppression is required, a modulator 'having the proper phase and frequency characteristics from 176 cycles to 3570 cycles (3570:cyc1es being three times the highest frequency dilference) must be used.

If telephone service (3."kc. fidelity) is contemplated, it might be expected that a maximum spurious output of -25 db would require a modulator capable of bcing'equalized for phase andfrequency irom lOO cycles to 6 kc. (two times 3 kc). However, when the characteristics of speech were analyzed, it was found that the higher frequencies have very low energy content and, therefore, do .notcreate appreciable high energy spurious output. It may be seen from this qualitative examinationthat phone service may require even less stringent modulator performance than does regular tone telegraph.

With regard to the transmitter of this invention, the spurious 'si'debands maybe balanced out to a level 30 toiO db below the level of one tone, when'two'tones are used for modulation. It is a reasonable estimate that a balance oi 30 db below'the level of one'tone, for two-tone modulation, can be maintained in practice, in a transmitter'constructed according to the teachings of this invention.

Figs. 7A, "7B and 7C taken together provide a detailed circuit diagram of the essential portions of the transmitter of this invention-to wit, all of the units in Fig. 5 except SSE generator i, frequency multiplier ll, amplifier l8, modulator power amplifier 24 and antenna 25. From a study of these figures, together with the legends thereon, the interrelation of these three figures, as well as the mode of operation of the circuits disclosed therein, will become apparent.

' What is claimed is:

l. In a transmitter, means for producing a single sideband signal in the form of a complex wave froma source of intelligence, said single sideband wave having amplitude modulation and phase modulation components, means for amplifying substantially only said phase modulation component, means for amplifying only the amplitude modulation envelope of said single sideband complexwave, and means for combining the amplified modulation envelope with the amplified phase modulation component to provide a resultant amplitude modulated and phase modulated wave representativeof said single sideband complex wave.

'2. In a transmitter, means for generating a single sideband signal, means for amplifying substantially only the phase modulation component of said signal, separate means for linearly amplifying only the amplitude modulation envelope of said signal, and means for combining the amplified modulation envelope with the amplified phase modulation component to provide a resultant amplitude modulated and phase modulated wave representative of the original single sidebandsignal.

3. In.,.a transmitter, means for generating a complex wave. which isiamplitude modulated and phase modulated byintelligence to be transmitted, means for substantially eliminating 'gamplitude variations from said complex wave to modulating the amplified resultant wave with the amplified detected modulation envelope.

4. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be transmitted, a limiter coupled to receive a portion of the output of said generating means to provide a resultant phase modulated wave at the limiter output, a nonlinear amplifier coupled to the limiter output, an amplitude modulation detector coupled to receive the remaining portion of the output of said generating means, a linear amplifier coupled to the output of said detector, and an amplitude modulator coupled to the output of said linear am lifier and to the output of said nonlinear amplifier to amplitude modulate the amplified resultant phase modulated wave with the amplified detected amplitude modulations.

5. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be transmitted, means for substantially eliminating amplitude variations from said complex Wave to provide a resultant phase modulated wave, means for am lifying said resultant wave, means for detecting the amplitude modulation envelope of said complex wave, means for am lifying said detected envelope, means for eifecting a predeterm ned time delay of the amplified detected amplitude modulation envelope, and means for amplitude modulating the am li ed resultant wave with the amplified delayed detected modulation envelope.

6. In a transmitter, means for generating a complex ave hich is am litude modulated and phase modulated b intelligence to be transmitted, means for el minating amplitude variations from said complex wave to provide a resultant hase m dule ted wave, means for amplifving said re ultant wave, means for detecting the amplitude modulations on said complex wa e, means for amplifying said amplitude modulations. means for amplitude modulating the amplified resultant ave with the amplified detected amplitude modulations to pro ide an output wave, and means for controlling the average power of said output wave in accordance with the energy level of said amplitude modulations.

'7. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be transmitted, means for eliminating amplitude variations from said complex wave to provide a resultant phase modulated wave. means for non linearl amplifying said resultant wave, means for detecting the amplitude modulation envelope of said com lex wave, separate means for linear- 1y amplifying the detected envelope, means for amplitude modulating at a high level the amplified resultant wave with the amplified detected modulation envelope, and means for linearly amplifying the modulated wave output of said last-named means.

8. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be transmitted, means for eliminating amplitude variations from said complex wave to provide a resultant phase modulated wave, means for nonlinearly amplifying said resultant wave, means for detecting the amplitude modulation envelope of said complex wave, separate means for linearly amplifying the detected envelope, means for eifecting a predetermined time, delay or the 75 a resultant amplitude modulated and phase.

12 amplified detected modulation envelope, means for amplitude modulating at a high level the amplified resultant wave with the amplified delayed detected modulation envelope, and means for linearly amplifying the modulated Wave out put of said last-named means.

9. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be transmitted, means for eliminating amplitude variations from said complex wave to provide a re sultant phase modulated wave, means for amplifying said resultant wave, means for detecting the amplitude modulation envelope of said complex wave, means for amplifying the detected envelope, means for amplitude modulating at a high level the amplified resultant wave with the amplified detected modulation envelope to provide an output wave, and means for radiating a wave representative of said output wave.

10. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be transmitted, means for eliminating amplitude variaions from said complex wave to provide a resultant phase modulated wave, means for amplifying said resultant wave, means for detecting the amplitude modulation envelope of said complex wave, means for amplifying the detected envelope, means for amplitude modulating the amplified resultant wave with the amplified detected modulation envelope to provide an output wave, and means, coupled to the output of said detecting means and operating on said amplitude modulating means, for controlling the average power of said output wave in accordance with the energy level of said detected modulation envelope.

11. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be transmitted, means for separating said wave into its amplitude modulation and phase modulation components and for deriving the amplitude modulation envelope from said wave, means for dividing in frequency the phase modulation component, means for amplifying and for multiplying in frequency the divided-frequency phase modulation component, and means for combining the amplitude modulation envelope of said complex wave with the amplified frequencymultiplied output of said dividing means to provide a resultant amplitude modulated and phase modulated wave representative of said complex Wave.

12. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be trans mitted, means for separating said wave into its amplitude modulation and phase modulation components, for deriving the amplitude modulation envelope from said wave and for applying such components to separate corresponding channels, means in the phase modulation channel for dividing in frequency the phase modulation component, means for amplifying and for multiplying in frequency the divided-frequency phase modulation component, means in one channel for equalizing the time delays of the signals passing through the two channels, and means coupled to both channels for combining the amplitude modulation envelope of said complex wave with the amplified frequency-multiplied output of said dividing means to provide '13 modulated wave representative "oi'xsaidccomplex wave.

13. A'transmitter according to elaiml2, whereill sald time delay e'qualizingimeans tcomprises a delay network in the I amplitude imodulation channel,

I l/In atransmitter, means ior generating 'a complex wave which is. amplitudefmodulated and phase modulated by intelligence to 1 be transmitted, means for :separating said wave .into its amplitude modulation and phase Smodulation components and for derivin lthe amplitude modulation envelope 1 from said Wave, :means for dividing in frequency bythe factorthaphase modulation component, means for amplifying and for multiplying. in, frequency by .the factor n the divided frequency phase modulation component; and means for-combining the amplitude modulation envelope of said complex wave with the amplified frequency multiplied output 1 of said dividing means'to provide a resultant 'amplitude modulated and "phase :modulated =wave representative of said "complex wave.

15. In a transmitter, means'for -generating-a complex Wave which: is amplitude modulatediand phase modulated by intelligence to be transmitted, means for'separating said wave into its amplitude modulation and phase modulation componentsand for deriving the ampiitude modulationenvelope from said wave, a frequency multiplier,1means for dividing inifre uency the phase modulation component and for thereafter applying. the same'to said irequencyflmultiplier, to thereby obtain rat. the output of said" multiplier a modulation index equal to that at the input of said'dividing means, and'means for combining theamplitude---modulation1 envelope l oi: said complex Wave with. the phasev modulation :component appearing at theeoutputuof said multiplier :to provide a resultantr amplitude modulated and phase modulated Wave representative of said complex wave.

16. In a transmitter, means forgenerating -a complex wave Whichis amplitude modulated and phase modulated by intelligence to-be transmitted, means for separating said wave: i-ntoits amplitude modulation and phase modulation components and for deriving the amplitude modulation.venvelope -from--said wave, means for dividing in. frequency the phase modulation component, means for 1 heterodyning the divided-frequency phasewmodulation component-to a different frequency, means for amplifying and for multiplying in frequency the, output of said hetero'dyning' means, and means for combining the amplitude modulation envelope, of saidcomplex' wave with the amplified frequency-multiplied' output of said heterodynin'g means to provide a resultant amplitude modulated and phase modulated wave representative of said complex wave.

1'7. In a transmitter, means for generating a complex wave which is amplitude modulated and. phase modulated by intelligence to be transmitted, means for separating said Wave into its amplitude modulation and phase modulation components, for deriving the amplitude modulation envelope from said Wave and for applying such components to separate corresponding channels, means in the phase modulation channel for dividing in frequency the phase modulation component, means for heterodyning the divided-frequency phase modulation component to a different frequency, means in the phase modulation channel for amplifying and for multiplying in frequencyathe output of said heterodyning'means, means in one channel for equalizing "the ritime (delays of the :signals passing throughithetwo.channels, and means coupledto both channels forcombining the amplitude modulationienvelopezofr said complex wave with the amplified,ffrequency multiplied output of said heterodyning means to provide a resultant "amplitude modulated andphase modulated wave representative of said complex wave.

'18.'In a transmitter, means for generating'a complex 'wave which is amplitude modulated and phase-modulated by intelli ence to be transmitted, means for separating said wave into its an p'litude modulation and phase modulation components? and for deriving'the amplitude modulation envelope fromsaid Wave, means for dividing in frequency 'by ithefactor n the phase modulation component, means for heterodyning the divided-frequency phase modulation component to a di-fferentfrequency, means for amplifying and fonmultiplying in frequency by the factor nthe output of said heterodyning means, and means for-combining the amplitude modulation envelope of said complex Wave with the amplified frequency-multiplied output of said heterodyning meanstoiprovide a resultant amplitude modulated and phasemodulated Wave representative ofsaid complex wave.

19... Inatransmitter, means for generating a complex wave which is amplitude modulated and phase Hmodulated icy intelligence to be trans mitted, means for separating said wave into its amplitude modulation and phase modulation components, for deriving the amplitude modulationlenvelope from said wave and for applying such components to separate corresponding channels, means in the phase modulation channellforldividing infrequency by theiactor n the lphase'modulation component, means for heterodyning the divided-frequency phase modulation component to a different frequency, means for amplifying and for multiplying in frequency by the factor n the output of said heterodyning means,..means in one channel for equalizing the time delays of the signals passing through the twochannels, and means coupled to both channels for combining the amplitude modulation envelopeof said complex Wave with the amplifled frequency-multiplied output of said heterodyning means to provide a resultant amplitude modulated :and phase modulated Wave representative of said complex Wave.

v20. Atransmitter according to claim 19, Whereinisaid time delay'equalizing means comprises a delay network in the amplitude modulation channel.

.21. In Vatransmittenmeans for generating a complex Wave which has amplitude modulation and phase modulation components, means for amplifying substantially only said phase modulation component, means coupled to said amplifying means for dividing in frequency the amplified phase modulation component, means for amplifying and for multiplying in frequency the divided-frequency phase modulation component, means for amplifying only the amplitude modulation envelope of said complex wave, and means for combining the amplified modulation envelope with the amplified frequency-multiplied output of said dividing means to provide a resultant amplitude modulated and phase modulated Wave representative of said complex wave.

22. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be transmitted, means for substantially eliminating amplitude variations from said complex Wave to provide a resultant phase modulated wave, means for dividing in frequency by the factor 11. said resultant Wave, means for amplifying and for multiplying in frequency by the factor n the divided-frequency resulant wave, means for detecting the amplitude modulation envelope of said complex Wave, means for amplifying said detected envelope, and means for amplitude modulating the amplified frequency-multiplied output of said dividing means with the amplified detected modulation envelope.

23. In a transmitter, means for generating a complex Wave which has amplitude modulation and phase modulation components, means for applying said Wave to two amplifying channels in one of which substantially only the phase modulation component is amplified and in the other of which only the amplitude modulation envelope of said complex Wave is amplified, means in the phase modulation channel for dividing in frequency the amplified phase modulation component, means for amplifying and for multiplying in frequency the divided-frequency phase modulation component, means for equalizing the time delays of the signals passing through the two channels, and means coupled to both channels for combining the amplified modulation envelope with the amplified frequency-multiplied output of said dividing means to provide a resultant amplitude modulated and phase modulated Wave representative of said complex wave.

24. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be transmitted, a limiter coupled to receive a portion of the output of said generating means to provide a resultant phase modulated Wave at the limiter output, means for dividing in frequency said resultant Wave, means for heterodyning the dividing-frequency resultant wave to a different frequency, means for amplifying and for multiplying in frequency the output of said heterodyning means, a nonlinear amplifier coupled to the output of said multiplying means, an amplitude modulation detector coupled to receive the remaining portion of the output of said generating means, a linear amplifier coupled to the output of said detector, and an amplitude modulator coupled to the output of said linear amplifier and to the output of said nonlinear amplifier to amplitude modulate the amplified phase modulated Wave With the amplified detected amplitude modulation envelope.

25. In a transmitter, means for generating a complex wave which is amplitude modulated and phase modulated by intelligence to be transmitted, means for substantially eliminating amplitude variations from said complex wave to provide a resultant phase modulated Wave, means for dividing in frequency said resultant wave, means for heterodyning the divided-frequency resultant Wave to a different frequency, means for amplifying and for multiplying in frequency the output of said heterodyning means, means for detecting the amplitude modulation envelope of said complex wave, means for amplifying said detected envelope, means for efiecting a predetermined time delay of the amplified detected modulation envelope, and means for amplitude modulating the amplified frequency-multiplied output of said heterodyning means with the amplified delayed detected modulation envelope.

26. In a transmitter, means for generating a complex Wave which is amplitude modulated and phase modulated by intelligence to be transmitted, means for eliminating amplitude variations from said complex Wave to provide a resultant phase modulated wave, means for applying said phase modulated Wave to a corresponding channel, means for detecting the amplitude modulation envelope of said complex wave and for applying such detected envelope to a separate corresponding channel, means in the phase modulation channel for dividing in frequency the phase modulated wave, means for heterodyning the divided-frequency phase modulated wave to a diiferent frequency, means for amplifying and for multiplying in frequency the output of said heterodyning means, means in one channel for equalizing the time delays of the signals passing through the two channels, means in the amplitude modulation channel for amplifying the detected envelope, means coupled to both channels for amplitude modulating the amplified frequency-multiplied output of said heterodyning means with the amplified detected modulation envelope to provide an output Wave, and means, coupled to the output of said detecting means and operating on said amplitude modulation means, for controlling the average power of said output Wave in accordance with the energy level of said detected modulation envelope.

LEONARD R. KAHN.-

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,020,327 Purington Nov. 12, 1935 2,098,307 Purington Nov. 9, 1937 2,261,643 Brown Nov. 4, 1941 2,383,847 Crosby Aug. 28, 1945 

